1. Field of the Invention
The present invention relates to a lens assembly, and in particular relates to a lens assembly with a fitting structure.
2. Description of the Related Art
FIG. 1 is an assembled cross section of a conventional lens module 1. The lens module 1 comprises a lens cylinder 11 and a lens assembly 12. The lens cylinder 11 has a light axis 100 and a cylindrical wall 111 enclosing the light axis 100. An accommodating space 112 is defined by an inner surface of the cylindrical wall 111 of the lens cylinder 11. The lens assembly 12 disposed in the accommodating space 112 comprises a first lens 121 having a first outer circumferential surface 123 and a second lens 122 having a second outer circumferential surface 124. A first clearance 101 is formed between the first outer circumferential surface 123 of the first lens 121 and the inner surface of the cylindrical wall 111 of the lens cylinder 11. A second clearance 102 is formed between the second outer circumferential surface 124 of the second lens 122 and the inner surface of the cylindrical wall 111 of the lens cylinder 11.
However, the following inconveniences are encountered when manufacturing the lens module 1. For example, all dimensions for the inner surface of the cylindrical wall 111 of the lens cylinder 11 as well as the first and second outer circumferential surfaces 123 and 124 must be precisely manufactured and fitted. If the tolerance of the first or second clearance 101 or 102 is inaccurate, the center of the first or second lenses 121 or 122 is not located at the light axis 100, resulting in resolution decrease and optical performance defects.
Furthermore, the first and second clearance 101 and 102 should be small and as equal as possible to increase the optical performance. Due to the requirement for the first and second clearance 101 and 102 to have small sizes, however, difficulty for installing the lens assembly 12 into the lens cylinder 11 is relatively increased and manufacturing yield is reduced.
FIG. 2 is an assembled cross section of a lens module 2 of Japanese Patent Application No. 3739295. The lens module 2 comprises a lens cylinder 21 and a lens assembly 22. The lens cylinder 21 has a light axis 200 and a cylindrical wall 211 enclosing the light axis 200. An accommodating space 212 is defined by an inner surface of the cylindrical wall 211 of the lens cylinder 21. The lens assembly 22 disposed in the accommodating space 212 comprises a single first lens 221 and two pieces of second lenses 222. The first lens 221 comprises an optical effective region 223a, a fixed region 224a encircling the optical effective region 223a, and an extending portion 225a extending from the circumference of the fixed region 224a in the direction of the light axis 200. Each of the second lenses 222 comprises an optical effective region 223b, a fixed region 224b encircling the optical effective region 223b, and an extending portion 225b extending from the circumference of the fixed region 224b in the direction of the light axis 200. Further, the extending portion 225a of the first lens 221 is provided with an outer circumferential surface 226a and an inner conical surface 227a, and the extending portion 225b of each of the second lenses 222 is provided with an outer circumferential surface 226b, an inner conical surface 227b and an outer conical surface 228.
A first clearance 201 is defined by the outer circumferential surface 226a of the first lens 221 and the inner wall surface of the cylindrical wall 211 of the lens cylinder 21, and a second clearance 202 is defined by the outer circumferential surface 226b of the second lenses 222 and the inner wall surface of the cylindrical wall 211 of the lens cylinder 21. The outer circumferential surface 226a of the first lens 221 is jacketed to the outer conical surface 228 of the extending portion 225b of the second lenses 222 and adjacent to the first lens 221, and the adjacent second lenses 222 are jacketed to each other at the inner conical surface 227b and the outer conical surface 228 therebetween. With respect to the structure of the lens module 2, only the first lens 221 and the inner wall surface of the cylindrical wall 211 of the lens cylinder 21 are utilized for tolerance fitting, i.e., only the first clearance 201 is needed to be controlled. Compared to the lens assembly 12 of the lens module 1 shown in FIG. 1, it is understood that the centers of the optical effective region 223a of the first lens 221 and the optical effective regions 223b of the second lenses 222 are easily kept at the light axis 200. However, the following inconveniences are encountered when manufacturing the lens module 2. The large-sized extending portions 225a/225b of the first/second lenses 221/222 are not suitable for application in mobile phones or thin and light cameras. Also, the costs of the raw material for manufacturing the extending portions 225a/225b of the first/second lenses 221/222 cannot be reduced.